1. Field of the Invention
This invention relates to a contact lens which is used for observing the fundus or eyeground with the aid of a slit lamp or the like.
2. Description of the Prior Art
When the eyeground is to be observed with the aid of a slit lamp, an auxiliary lens such as an eyeground inspecting contact lens, or a ruby lens having a great negative refractive power, or an auxiliary lens like a bayadi lens having a great positive refractive power is used to correct the refractive power of the eye.
Observation of the eyeground always involves the necessity of illuminating the eyeground to be observed and, therefore, part of the illuminating light flux is reflected by the auxiliary lens or by the surface of the cornea and this greatly interferes with the observation.
For this reason, the most popular known eyeground inspecting contact lenses have been those having a single boundary surface with respect to the air, that is, having only one surface that produces the harmful reflected light. However, these known lenses have been characterized by the cumbersomeness with which such contact lenses are mounted to the corneas of the eyes to be inspected.
A typical eyeground inspecting contact lens according to the prior art is shown in FIG. 1 of the accompanying drawings wherein numberal 1 designates the eye to be inspected, and 2 denotes the eyeground inspecting contact lens formed in a conical shape which has one end face adapted for intimate contact with the cornea surface of the eye to be inspected, and the other end face 2' serving as the incidence surface for the illuminating light flux. Designated by 3 is a light source (or an optical system) for illuminating the eyeground, and 4 an inspector's eye (or an eyeground observing optical system). Numberal 5 indicates a condenser lens and 6 a half-mirror by which the light flux passed from the light source 3 through the condenser lens 5, is directed toward the contact lens 2. X-X' is the observation axis on which the inspector's eye 4 may observe the fundus of the eye 1 to be inspected.
Inspection of the fundus or eyeground is carried out with the inspecting contact lens 2 mounted on the eye 1 to be examined, as shown in FIG. 1, and the observation of the eyeground requires the eyeground to be illuminated by the light source 3 as already described. However, part of the illuminating light flux is reflected by the incidence surface 2' of the inspecting contact lens 2 and enters the inspector's eye 4 to interfere with his observation (as indicated by R in FIG. 1).
In recent surgical operations photo-concentration techniques have been utilized in which a flux of intense light from a xenon lamp or a laser is focused on the eyeground to burn the same, but in this case, if the harmful reflected light as described above should occur at all, it would not only cause interference with the observation, but would also be very dangerous to the inspector's eye.